The present invention relates to novel polymers useful, for example, for preparation of resist compositions used for production of semiconductor devices, etc., and novel acrylic or methacrylic acid derivatives usable as materials for said polymers.
Novolak resins and polymers comprising acrylic acid units or methacrylic acid units have been known as alkali-soluble resins. of these, various polymers have been put to practical use as materials for photolithography or materials for electronics industry, such as resist materials. Particularly in the lithography field, g-line light sources (wavelength 436 nm), i-line light sources (wavelength 365 nm) for ultraviolet light, and recently excimer lasers (KrF excimer laser: wavelength 248 nm, ArF excimer laser: wavelength 193 nm) are used as a light source for exposure. As the base polymer of a resist material suitable for each of these light sources, novolak resins are mainly used in resists for i-line or g-line light and phenolic resins are mainly used in resists for KrF excimer laser beams. Both the novolak resins and the phenolic resins have phenolic hydroxyl groups (pk.sub.a : about 12) as functional groups which permit development with an alkali developing solution.
On the other hand, acrylic acid derivative or methacrylic acid derivative resins are leading base polymers used in resist materials for ArF excimer laser beams which are under development (for example, JP-A 7-199467, JP-A 8-82925, JP-A 7-234511, etc.).
The reason is that conventional resins having aromatic rings have a low transparency in the deep ultraviolet region and are quite opaque at 193 nm, the wavelength of ArF excimer laser beams.
The resist materials obtained by using the acrylic or methacrylic resin as the base polymer, however, have a high acidity (pk.sub.a : about 5) because of their carboxylic acid groups as soluble groups and hence have a much rapider dissolution rate in alkali development than do the conventional polymers having phenolic hydroxyl groups as soluble groups. Therefore, they are disadvantageous in that when a 2.38% aqueous tetramethylammonium hydroxide (TMAH) solution, a conventional alkali developing solution is used without dilution, film peeling or dissolution of non-exposed portion occurs in the formation of a fine pattern, so that no satisfactory pattern can be obtained.
Moreover, the above-mentioned 2.38% TMAH is a leading alkali developing solution employed at present in an actual production line of semiconductor devices, so that it is very difficult to use a diluted developing solution in a production line in which there is used a combination of resist materials of different generations, such as a combination of a resist for i-line light and a resist for KrF excimer laser beams or a combination of a resist for KrF excimer laser beams and a resist for ArF excimer laser beams.